ToddW,
Spence gave you a good link to a thread where we talked about these flat cars and some of the problems. If you take a look at my post in that thread you will see that you can make these flat car real nice, with the addition of the MTH Primer trucks.
With this alteration the flat cars become a quality entity and run well.
Bill T just started a nice thread on fixing these flat cars, you might want to give it a gander, he fixes the cars and adds a load to give the cars decent weight to run.
PCRR/Dave